[Tracking Requested - why for this release]: significant perf regression Under condition of image.high_quality_downscaling.enabled = false Scrolling speed has become 200% slower after landing Bug 1044702. Steps To Reproduce: 1. Set image.high_quality_downscaling.enabled = false 2. Open testcase index.html https://dl.dropboxusercontent.com/u/33246373/20140922031026.7z 3. Run the following code in ScratchPad with chrome privilege (function() { function scroll(event) { var top = content.document.documentElement.scrollTop || content.document.body.scrollTop; if (top < 11000) { var evt = content.document.createEvent("KeyboardEvent"); evt.initKeyEvent ("keypress", true, true, window, null, null, null, null, 40, 0) content.document.dispatchEvent(evt) } else { content.removeEventListener("scroll", scroll, false); content.scrollTo(0,0); alert(new Date().getTime() - start); } } content.focus(); content.scrollTo(0,0); var start = new Date().getTime(); content.addEventListener("scroll", scroll, false); scroll(); })(); Actual Results: The scrolling speed has become slow, 200% slow. Regression window(m-i) Good: 4500-5000 msec https://hg.mozilla.org/integration/mozilla-inbound/rev/80164e15bd54 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 ID:20140912024553 Bad: 14000-15000 msec https://hg.mozilla.org/integration/mozilla-inbound/rev/c232720a2847 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 ID:20140912025257 Pushlog: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=80164e15bd54&tochange=c232720a2847 Regressed by Bug 1044702 - Use Moz2D source clipping when we can. r=Bas

This was fixed by 1412188703 Bug 902952.